1. Field of the Invention
The present invention relates to a production method of three-dimensional data of a dental prosthesis for cutting a block for cutting the dental prosthesis by an automatic cutting machine by using a three-dimensional measuring device so as to have the same shape as a measured object.
2. Description of the Conventional Art
As a general production method of the dental prosthesis such as an inlay, a crown, a bridge or the like, the following methods have been widely known. A method comprises casting of a metallic material by a lost wax casting method, to thereby produce the dental prosthesis. Another method comprises building up of a ceramics material on a refractory model, and baking of it in a vacuum electric furnace, to thereby produce the dental prosthesis for the purpose of aesthetic appreciation, such as a ceramic inlay, an all ceramic crown or the like.
However, as for the work for producing the dental prosthesis by the conventional method such as the lost wax casting method, the baking by the vacuum electric furnace or the like, almost all processes are carried out by a manual labor by a dental technician. Further, the process by the manual labor is remarkably fine and complicated. Thus, such the process takes remarkable time and effort, and the quality of the dental prosthesis is influenced by the level of a skill of the dental technician.
Then, as a method for producing much more dental prosthesis having even quality in a short time without depending on the manual labor of the dental technician, a dental CAD/CAM system for producing the dental prosthesis has been developed in recent years. In this technique, the dental prosthesis is produced by the steps of producing the three-dimensional shape data of the dental prosthesis such as the inlay, the crown, the bridge or the like by using a three-dimensional measuring device, a computer or the like, and cutting the block for cutting of the dental prosthesis by an automatic cutting machine on the basis of the obtained three-dimensional shape data of the dental prosthesis.
As such the three-dimensional measuring device in the dental CAD/CAM system, for example, a device comprising a holding base for the measured object, a rotating jig for the holding base, a changing jig for a holding base rotating shaft, a changing jig for a holding base position, and a laser measuring part, is used (for example, referring to Japanese Patent Application Laid Open No. 5-332731).
Such the device is effective when a small measured object is measured to thereby produce the three-dimensional shape data of the dental prosthesis. The small measured object is a small type dental prosthesis applied to only one tooth, such as the inlay, the crown or the like. However, the device has a structure where only the holding base of the measured object is rotated by the rotating jig, so that there is a problem that the large size measured object cannot be measured. The large size measured object is a model of a large-sized type dental prosthesis applied to a plurality of teeth, such as the bridge or the like, or a gypsum model of a plurality of remaining teeth, or the like.
Then, for example, the following three-dimensional devices capable of measuring the large size measured object to thereby produce the three-dimensional shape data, has been developed, where the large size measured object is the model of the large size dental prosthesis applied to the plurality of teeth, such as the bridge or the like, or the gypsum model of the plurality of remaining teeth, or the like. One device comprises a body base, a rotary stage, an X and Y stage, a drive control means, a measured object holding means, an R stage, a first laser displacement gauge, a Z stage, and a second laser displacement gauge (for example, referring to Japanese Patent Application Laid Open No. 7-181022). In this device, the X and Y stages are movable in the specified horizontal direction X and the horizontal direction Y orthogonal to the direction x independently from the rotation of the rotary stage, and has a fitting part for fitting with another member. The drive control means controls the drives of the rotary stage and the X and Y stages respectively. The measured object holding means has a part to be fitted with a fitting part of the X and Y stages, and a fitting part for fitting with the measured object. The R stage is movable in the diameter direction of the rotary stage. The first laser displacement gauge provided at the under face of the R stage so as to make its optical axis to be parallel to a rotating shaft of the rotary stage. The Z stage is movable in the direction parallel to the rotating shaft. The second laser displacement gauge is provided at the side face of the Z stage so as to cross orthogonally with the rotating shaft. Another device comprises an Xθ and Yθ stage, a first drive means, an X and Y stage, a fixing tool, a second drive means, an optical probe, and a computer (for example, referring to Japanese Patent Application Laid Open No. 2002-257511). In this device, the Xθ and Yθ stages are rotated in Xθ and Yθ directions. The first drive means finely drives these Xθ and Yθ stage in respective directions. The X and Y stage moves in X and Y directions on the Xθ and Yθ stage. The fixing tool fixes the measured object having the spherical face on the X and Y stage. The second drive means finely drives the X and Y stage in respective directions. The optical probe measures the three-dimensional coordinate values of the face of the measured object. The computer controls the first drive means and the optical probe, and arithmetically processes signals.
Such the devices can measure the large size measured object and make the three-dimensional shape data, where the object is the model of the large size dental prosthesis applied to the plurality of teeth, such as the bridge or the like, or the gypsum model of the plurality of remaining teeth, or the like. However, the device is complicated itself, difficult to be controlled, and at high production cost. Further, since the former device has two laser displacement gauges, there are problems that the maintenance and production costs are high.
Then, the three-dimensional measuring device capable of measuring from the small measured object to the large measured object, and decreasing the production and maintenance costs by having one laser sensor for measuring the shape of the measured object, is developed, where the small measured object is the model of the small type dental prosthesis applied to small number of teeth, such as the inlay, the crown or the like, and the large measured object is the model of the large type dental prosthesis applied to large number of teeth, such as the bridge or the like, or the gypsum model of large number of remaining teeth, or the like. This device comprises a rotary table, an XY table, and a measuring part for measuring the three-dimensional coordinates of the shape of the measured object. In this device, the rotary table has a rotating shaft, with an axis being Z axis. The XY table is arranged on the rotary table, movable in the X axial direction and the Y axial direction, and has a placing table fixed on the upper part thereof, where the placing table is for providing a measured object mounting tool thereon in a specified direction. The measuring part measures the three-dimensional coordinates of the measured object shape mounted to the measured object mounting tool on the placing table by one laser sensor, which at least can rotationally move on one plane containing the Z axis around a desired point on the Z axis.
As a method for measuring the model of the dental prosthesis such as the inlay, the crown, the bridge or the like to thereby produce the three-dimensional shape data by such the device, for example, the following methods have been carried out. One method comprises, providing the model of the dental prosthesis on the placing table in the three-dimensional measuring device so as to direct its jawbone side to the side direction, measuring it, and thereby making the three-dimensional shape data. The model of the dental prosthesis is formed with a wax, a synthetic resin or the like. The jawbone side is to be engaged with an abutment tooth. (Hereinafter, this method is referred to as “the former production method of the three-dimensional shape data”.) Another method comprises, providing the model of the dental prosthesis on the placing table in the three-dimensional measuring device in the state of the model being engaged with a model of an abutment tooth or a model of an alveolar ridge, measuring the model of the dental prosthesis, removing then the model of the dental prosthesis, measuring a part, where the model of the dental prosthesis is contacted, in the model of the abutment tooth or the model of the alveolar ridge, and thereby producing the three-dimensional shape data of the model of the dental prosthesis on the basis of the each measured values. The model of the dental prosthesis is formed with the wax, synthetic resin or the like. (Hereinafter, this method is referred to as “the latter production method of the three-dimensional shape data”.)
Each of the above production methods of the three-dimensional shape data is sufficiently used, when making the three-dimensional shape data of the dental prosthesis by measuring the model of the dental prosthesis such as the inlay, the crown, the bridge or the like, which does not need the comparatively high measuring accuracy and processing accuracy, to thereby make the dental prosthesis by cutting the block for cutting of the dental prosthesis by the automatic cutting machine on the basis of the produced three-dimensional shape data of the dental prosthesis. However, when making the dental prosthesis which need to have a remarkably high measuring and processing accuracies, for example, the dental prosthesis for an implant applied to only one implant fixture, both of the above production methods of the three-dimensional shape data have the problems that it is remarkably difficult to produce the dental prostheses having the necessary dimensional accuracy.
More particularly, the dental prosthesis for the implant applied to only one implant fixture is provided and fixed at an intra-oral side part of the implant fixture embedded into the jawbone, directly or through the abutment. An engaging portion engaged with the intra-oral side part of the implant fixture is projected and/or recessed on the jaw bone side of such the dental prosthesis for the implant, so as to provide the dental prosthesis at a desired rotational position around the axis of the implant fixture, when the dental prosthesis is fixed at the intra-oral side part of the implant fixture.
As for the engaging portion projected and/or recessed on the jaw bone side of the dental prosthesis for the implant, an engaging part is formed to have a sectional shape other than that of a rotary body (hexagonal pillar shape or recessed shape in general). Thus, when the three-dimensional shape data of the model of the dental prosthesis for the implant is produced by the above described former production method of the three-dimensional shape data, there is a problem that the engaging portion cannot be accurately measured, since laser light of the laser sensor of the measuring part can not reach to the inner part of the engaging portion, and the placing table or the XY tables becomes an obstacle, when measuring the part placed on the placing table side of the engaging part. On the other hand, when the three-dimensional shape data of the model of the dental prosthesis for the implant is produced by the above described latter production method of the three-dimensional shape data, the both measured values of the portion on the engaging portion side of the model of the dental prosthesis and the other portion than the engaging portion side thereof are measured by dividing two times respectively. Thus, when the three-dimensional shape data of the model of the dental prosthesis is produced on the basis of these values, there is a problem that the possibility for producing the mismatched three-dimensional shape data is remarkably high, that is, the three-dimensional shape data, where the position of the engaging portion is deviated with respect to the other portion, may be made. Further, there are problems that, when such the deviation is even slightly generated, the dental prosthesis interferes the adjacent tooth at the time of fixing the actually produced dental prosthesis at the implant fixture and that, in the worst case, the produced dental prosthesis cannot be fixed at the implant fixture to become a waste.
Further, the engaging portion of the dental prosthesis for the implant has a polygonal shape having corner parts, for example, regular hexagon in general, so that there is a problem that it is difficult to accurately measure this engaging portion by the laser sensor of the general three-dimensional measuring device. Further, if the produced three-dimensional shape data of the engaging portion of the dental prosthesis is even slightly differed from the actual shape of the engaging portion of the model of the dental prosthesis, there may be problems that the dental prosthesis cannot be engaged well with the implant fixture, or is loosened after fixing with the implant fixture, if the dental prosthesis, which is made by cutting the block for the dental prosthesis by the automatic cutting machine on the basis of the inaccurate three-dimensional data of the dental prosthesis, is fixed with the implant fixture.
Further, even when the former or latter production method can obtain the accurate three-dimensional shape data of the model of the dental prosthesis, there is a problem that the dental prosthesis as the produced three-dimensional shape data cannot be accurately produced when the engaging portion has the shape having the corner parts, since the automatic cutting machine is used for cutting the block using rotationally cutting tool in general, where the automatic cutting machine makes the dental prosthesis on the basis of the three-dimensional shape data of the model of the dental prosthesis.